Magnetic core with variable air gap



Feb. 8, 1949. A. M. CANDY MAGNETIC CORE WITH VARIABLE AIR GAP Filfld Dec. 22, 1947 0,0,0 0 a m c a mu '0'. u o

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Patented Feb. 8, 1949 MAGNETIC cons wu'n VARIABLE am car Albert M. Candy, La Grange, llL, assignor, by mesne assignments, National Cylinder Gas Company, Chicago, 111., a corporation of Dela- Application December 22, 1947, Serial No. 793,158

My invention relates, generally, to magnetic control systems and it has particular relation to provide for varying the length of an air gap in a magnetic circuit in such manner that the length of the air gap is uniform over the entire area of the juxtaposed surfaces which constitute the boundaries of the air gap. This is accomplished by shaping the juxtaposed surfaces so that, as they are rotated relative to each other this relationship is maintained. The particular shape of surface which provides this relationship is an involute of a base circle. Where solids are involved the surfaces are involute surfaces of a base cylinder whose longitudinal axis coincides with the axis of relative rotation of the members.

Among the objects of my invention, as disclosed herein, are: To provide a magnetic circuit having a plurality of air gaps whose lengths are varied uniformly and the magnetic circuit makes optimum use of the material of which the same is constituted; to employ a rotor having an involute surface for uniformly and simultaneously varying the length of three air gaps in the magnetic circuit; to employ a three legged magnetic core for the magnetic circuit with the rotor cooperating with each leg; to provide a winding on the middle leg the magnetic flux through which is varied on movement of the rotor; and to construct the middle leg so that its cross sectional area equals the sum of the cross sectional areas of the end legs.

Other objects of my invention will, in part, be

obvious and in part appear hereinafter.

My invention is disclosed in the embodiment thereof shown in the accompanying drawing and it comprises the features of construction, combination of elements and arrangement of parts which will be exemplified in the construction hereinafter set forth and the scope'of the application of which will be indicated in the appended claims.

For a more complete understanding of the nature and scope of my invention reference may be had to the following detailed description, taken together with the accompanying drawing in which:

Figure 1 isa view, in side elevation, of a magnetic control device constructed in accordance with my invention;

Figure 2 is a detail sectional view, at an enlarged scale, taken along the line 2-2 of Figure l; and

Figure 3 illustrates diagrammatically how the magnetic control device shown in Figure i can be employed for varying the current flow in an arc welding circuit.

Referring now particularly to Figure l of the drawing, it will be observed that the reference character It designates, generally, a magnetic core structure that is formed of laminated transformer steel. The core structure i0 includes a stator which is indicated, generally, at H. The stator Ii comprises a middle leg 12 and end legs I! and it. In order to work the material constituting the stator ii at the highest eificiency the cross sectional area of the middle leg I2 is equalto the sum of the cross sectional areas of the end legs l3 and it. This arrangement is provided since the flux flowing through the middie leg i2 is. divided equally between the end legs i3 and I. As shown, the middle leg i2 and the end legs i3 and M are joined by a common member H in accordance with conventional practice.

With a view to varying the magnetic flux in the core structure it a rotor i5 is employed which has an involute surface i5 whose base cylinder is indicated at IT in Figure 3. In my copending application above referred to, the manner in which the involute surface 16 is generated is described in more detail. Accordingly, the same is omitted here.

It will be noted in Figure 1 that the ends of the legs i2, i3 and id have surfaces l8, l9 and 2%, respectively, which are juxtaposed to the surface is and are similarly shaped so that the air gaps 2!, 22 and 23 therebetween can be varied simultaneously and uniformly as the rotor i5 is rocked about the longitudinal axis of the base cylinder il in a manner to be described presently. As the rotor i5 is rotatedclockwise from its position shown in Figure 3 toward the position shown in Figure 1 and beyond, the length of each of the air gaps 2 i, 22 and 23 is increased simultaneously, uniformly and equally. That is, since the rotor I 5 has an involute surface It and the juxtaposed surfaces [8, l9 and 20 of the legs I2, is and i6 conform thereto. for any position of the rotor i5, the length of each of the air gaps 2i, 22 and 23 will be uniform and equal over the entire area of the surfaces i8, i9 and 20. Therefore, there is no concentration of flux or a shifting of flux on surfaces l3, l3 and as the rotor I5 is swung away from the position shown in Figure 3 but rather there is a uniform variation in the amount of magnetic flux in the core structure ID, the extent of the variation depending of course upon how far the rotor I5 is moved away from the position shown in Figure 3.

A winding, shown generally at 24, may be mounted on the core structure l3 and around the middle leg l2. As will appear hereinafter the winding 24 is arranged to be energized from a suitable source of alternating current and it is connected to function as a variable inductor as a result of shifting of the position of the rotor I 5.

Any suitable means can be employed for rockably mounting the rotor l5. As shown in Figure 2 the rotor Hi can be mounted on a shaft and secured thereto against rotation by a key 23. The ends of the shaft 25 extend through plates 21 and 23 of non-magnetic material which may be secured to opposite sides of the core structure it by through bolts 23. Spacer rings 33 and 3| serve to space the rotor l5 from the plates 21 and 23 in which the shaft 25 is journaled.

The rotor l5 can be controlled from a remote point or it can be rotated directly by a hand wheel 32 which is slidable on the outer end of the shaft 25 but is prevented from relative rotation therewith by a key 33.

It is desirable to lock the rotor ii in any position to which it may be adjusted in order to prevent its being shifted as a result of the rotational force exerted thereon by the magnetic flux inv the core structure III. For this purpose the outer end 34 of the shaft 25 may be threaded for receiving a nut 35 which has an arm or handle 35 to facilitate its rotation. Between the nut 35 and the hub of the hand wheel 32 is a washer 31. The washer 31 has a finger 38 which enters a slot 33 in the outer end 34 of the shaft 25 to prevent relative rotation. When the nut 35 is tightened against the washer 31, it forces the hub of the hand wheel 32 against the adjacent face of the plate 21. The gripping action exerted therebetween is sufficient to prevent rotation of the rotor i5 until the nut 35 is backed off on the shaft 25.

Referring now particularly to the diagrammatic representation in Figure 3 it will be observed that the winding 24 comprises winding sections 42 and 43. These sections 42 and 43 have diflerent numbers of turns in order to provide different current ranges when the device is employed for varying current flow in a circuit such as a welding circuit. For illustrative purposes it is pointed out that the winding section 42 may comprise twenty-three turns while the winding section 43 may comprise seven turns. With the section 42 only connected in a load circuit, the current flow therethrough can be varied from 200 amperes when the rotor 15 oocupies the position where the air gaps 2i, 22 and 23 are of maximum length to about '15 amperes when it is rotated to a position providing minimum air gap length in the core structure N as shown in Figure 3. Similarly when the winding sections 42 and 43 are connected in series in the load circuit and the rotor I5 is moved in a similar fashion the current can be-varied from a maximum of about 100 amperes to a minimum of about 20 amperes. stood that these values are merely indicative of what can be accomplished in practicing my in- It will be under- 4 ventlon and are not to be considered as limiting its .application in any way.

' In order to facilitate making electrical connections to the winding sections 42 and 43 certain of their end turns are brought out to sockets 45 and 41 as shown.

It will be noted in Figure 3 that the load circuit may be a welding circuit which is indicated, generally, at 43 of the arc welding type. The weld-' ing circuit 43 may be energized from a source 43 of alternating current, such as a 60 cycle source. The source 43 may be connected to energize a primary winding 53 of a transformer, shown generally at 5|, having a secondary winding 52 which energizes the welding circuit 43, through winding 42 or through windings 42 and 43 in series.

One terminal of the secondary winding 52 may be connected by a conductor 53 to one terminal of the winding 42. A plug 51 may be employed for insertion in the socket 45 or 41 and it may be connected to a conductor 53 which extends to a welding electrode 53. An are 60 can be maintained between the welding electrode 59 and work ii on which the welding operation is to be performed. The work 3| may be connected by a conductor 62 to the other terminal or the secondary winding 52. It will be understood that the current flowing in the welding circuit 43 can be varied by shifting the position of the rotor l5 with respect to the stator ll.

When it is desired to use the winding section 42 only, and the higher current range for the same, the plug 51 is inserted in the socket 45. The current flowing in the welding circuit 48 then can be varied by rocking the rotor l5 as described. For the lower current range the plug 51 is withdrawn from the socket 45 and inserted in the socket 41. This connects the winding sections 42 and 43 in series with the welding circuit 43.

With a view to indicating the current flow which is available for any given setting of the rotor i5, scales 53 and 64 may be provided for cooperation with pointers 55 and ,31 that may be carried by an arm 63 which rotates with the rotor i 5. When the winding section 42 is connected in the welding circuit 43, the scale 83 may be read while the scale 54 may be read when the winding sections 42 and 43 are connected in series in the welding circuit 43. Obviously a single scale can be employed with a suitable multiplying factor orother well known means can be employed for indicating the current flow for any position of the rotor l5 and any arrangement of the winding sections 42 and 43.

Since certain further changes can be made in the foregoing construction and different embodiments of the invention can be made without departing from the spirit and scope thereof, it is intended that all matter shown in the accompanying drawing and described hereinbefore shall be interpreted as illustrative and not in a limiting sense.

I claim as my invention:

1. In combination, a magnetic core structure comprising a central leg and end legs on opposite sides thereof, and a relatively rotatable member for coacting with said legs to change the lengths of the air gaps therebetween, the surface of said member constituting one terminus other terminus of each air gap substantially coinciding with the juxtaposed surface of said member whereby on relative rotation of said legs and said member the length of each air gap is uniform and equal over the area of the juxtaposed surfaces at any relative position of said legs and member; and an electrically energizable Winding on said core structure.

2. The invention, as set forth in claim 1, wherein the legs constitute a generally rectangular core structure with the central leg having a cross sectional area substantially equal to the sum of the cross sectional areas of said end legs.

3. The invention, as set forth in claim 2, wherein the winding is located on the central leg.

4. The invention, as set forth in claim 3, wherein the legs are stationary and the member is rotatable.

5. The invention, as set forth in claim 4, where- 6 in locking means cooperate with the member to hold the same in any operative position.

6. The invention, as set forth in claim 2, wherein windings are located on more than one leg.

ALBERT M. CANDY.

REFERENCES CITED 7 The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,699,142 Hendricks Jan. 15, 1929 2,431,860 Friedlander Dec. 2, 1947 FOREIGN PATENTS Number Country Date 441,751 Great Britain Jan. 24, 1936 

